The purpose of this research is to investigate the extent to which the relative contributions of genetic and levels of hierarchically organized traits show more change than others. Personality data from three major assessment instruments (Eysenck's Personality Questionnaire, Cloninger's Tridimensional Personality Questionnaire, and the Karolinska Scales of Personality-to approximate J. Gray's model) provide the basis for multivariate investigations of personality structure in adulthood. -- response to NIH PA-98-076 (Behavior Genetics in Adulthood and Old Age), we propose secondary analyses of this unique item pool obtained on a large sample (N = 4119 individuals) of older adult twins 50 to 96 years of age. Our investigations will: 1) examine the phenotypic factor structure of the different personality dimensions within and across these three models of personality; 2) use biometrical analysis of twin data to estimate the genetic and environmental sources of variance in the primary facets/subscales and higher-order personality dimenions; 3) assess the factor invariance and/or changes in the genetic and environmental architecture of comparable personality factors across age-cohorts; 4) evaluate the joint factor structure underlying the three personality models through biometrical analysis of the combined facet and item-level data pool; 5) apply quantitative genetic methods to optimize factor structure for maximal genetic and environmental sources of variance; and 6) evaluate the external (i.e., predictive) validity of the existing and derived personality scales. The overarching goal of our multivariate investigations is to improve the measurement of personality concepts for gerontologically-relevant research.